ML20210E169
| ML20210E169 | |
| Person / Time | |
|---|---|
| Issue date: | 02/03/1987 |
| From: | Stello V NRC OFFICE OF THE EXECUTIVE DIRECTOR FOR OPERATIONS (EDO) |
| To: | Chilk S NRC OFFICE OF THE SECRETARY (SECY) |
| References | |
| NUDOCS 8702100242 | |
| Download: ML20210E169 (4) | |
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UNITED STATES 1
NUCLEAR REGULATORY COMMISSION f
y wasuemorow.o.c.sosas FEB 0 31987 i
l MEMORANDUM FOR: Samuel J. Chilk Secretary of the Commission FROM:
Victor Stello, Jr.
Executive Director for Operations
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SUBJECT:
REPORT ON PROGRESS AND SCHEDULE OF NRC PROGRAM
. PLAN RELATING TO CLARIFICATION OF U. S. GEOLOGICAL SURVEY POSITION REGARDING SEISMIC DESIGN EARTHQUAKES IN THE EASTERN SEABOARD OF THE UNITED STATES During the December 17, 1986 Commission meeting to discuss implementation of the severe accident policy statement, the Connission requested that they be 1-updated on staff efforts and schedule regarding clarification of the U. S.
Geological Survey (USGS) position with respect to the Charleston earthquake.
In response to that request and to your memorandum of January 5,1987 the following infonnation is provided.
For the purpose of licensing nuclear facilities in the southeastern United States, the NRC staff has taken a position, based primarily on the advice of 4
the USGS, that any reoccurrence of the 1886 Charleston, South Carolina earthquake would be confined to the Charleston area; that is, the Charleston earthquake is assumed to be associated with a geologic structure in the Charleston area. The effect of this position is that nuclear power plants in the region east of the Appalachian Mountains are usually controlled in their seismic design, according to Appendix A to 10 CFR Part 100, by the maximum historical earthquake not associated with a geologic structure. This controlling earthquake is typically a Modified Mercalli Intensity (MI) VII or VIII whereas the Charleston earthquake was a MMI X.
Since 1974, the NRC has funded an extensive research project to gain further information on the causative mechanism of the Charleston earthquake.
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In a letter dated November 18, 1982 from James F. Devine, USGS to Robert E.
Jackson, NRC, the USGS clarified its position indicating that:
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',L 4 "Because the geologic and tectonic features of the Charleston region are similar to those in other regions of the eastern seaboard, we conclude i
that although there is no recent or historical evidence that other regions have experienced strong earthquakes, the historical record is not, of itself, sufficient grounds for ruling out the occurrence in these
.other regions of strong seismic ground motions similar to those experienced near Charleston in 1886. Although the probability of strong ground motion due to an earthquake in any given year at a particular location in the eastern seaboard may be very low, deterministic and probabilistic evaluations of the seismic hazard should be made for individual sites in the eastern seaboard to establish the seismic l
engineering parameters for critical facilities."
In a Commission Paper dated February 5,1982 (SECY-82-53), we informed the Commission of the possibility of modification in the USGS position. In a memorandum dated November 19, 1982, th~e USGS clarification was forwarded to l
the Comission along with an assessment of significance and a preliminary plan l
to address the clarified USGS position. This plan was discussed with the Comission in its November 19, 1982 meeting and a joint NRR/RES program was 3
l initiated. The joint program consisted of a short term probabilistic program that has as its core a Lawrence Livemore Laboratory (LLNL) estimation of seismic hazard at all nuclear power plant sites east of the Rocky Mountains, and a long tem deterministic program through RES to detemine the causes of larte earthquakes, such as the Charleston earthquake, along the eastern sealoard.
As a means of comparison to the LLNL calculations we recomended in our original program plan that a utility sponsored study also be carried out.
This study has been carried out by the Electric Power Research Institute l
(EPRI) under sponsorship of a Seismicity Owners Group (50G). In a memorandua l
to the Comission dated December 24, 1984, we indicated that the probabilistic portion of the plan to address the clarification in the USGS position would be available at the end of 1986 in order to await completion of the EPRI program and allow a thorough comparison of EPRI and LLNL seismic hazard estimates at 10 test sites.
In 1985 and 1986, meetings and workshops were held with EPRI, LLNL and the USGS to discuss these and other seismic hazard estimates. A draft LLNL report was issued providing a detailed comparison of the two studies and in July 1986 the SOG submitted the EPRI study for review as a topical report. This review is presently underway and is expected to be completed in mid 1987 pending receipt of all portions of the EPRI study and responses to staff and USGS questions. Present comparisons between the EPRI and LLNL studies at the 10 test sites indicate that the differences that do exist are more related to ground motion estimation models than to differences in the assumed sources of earthquakes. It also appears that these differences have a comparatively minor effect on the relative ranking and comparison of seismic hazard among
i the various sites. This is encouraging since the staff's program plan relied upon the use of relative comparisons of probabilistic seismic hazard from site to site and from region to region.
Due to the comparison and delays it was felt appropriate to repoll the LLNL experts. This is proceeding and probabilistic seismic hazard calculations are expected to be completed and reported on by the end of 1987. These results will be evaluated by the staff and compared with any additional results j
available from utility sponsored EPRI calculations, from sensitivity studies carried out by the USGS and from other sources. This evaluation is expected to be completed by June 1,1988 and as indicated in the original staff plan i
may result in the identification of several plants which may need additional engineering analysis.
Ultimate resolution of the problem of larfle damaging earthquakes along the eastern seaboard of the United States wil reside in the long-term determin.
istic program. ~ Investigations thus far have found evidence of paleolique-faction from moderate to large prehistoric earthquakes that may have affected an area larger than that affected by the 1886 Charleston event. These in-l vestigations are continuing and additional studies will help define the locations and extent of the areas involved, the size of earthquakes which caused the paleoliquefaction and the recurrence intervals that are associated with them. We will keep the Connission infomed of any sifinificant new developments in both the probabilistic and deteministic e ements of this program.
1 Criginal cienc A, g7' yictor Stollo u
f Victor Stello, Jr.
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Executive Director i
for Operations Distribution Central File DSRO Chron File JRoe fM RPAB Reading File Victor Stello, Jr.
TRehm i
H. Denton R. Vollmer JSniezek T. Speis B. Sheron EDO r/f F. Congel R. Barrett L. Reiter D. Mossburg (WITS 870003)
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